1. Field of the Invention
The present invention relates to electronic systems employing CD-ROM or DVD readers as read-only storage devices. More particularly, the present invention relates to a method and apparatus for reducing or eliminating read errors from such storage devices.
2. The Background Art
Modern electronic systems such as video playback machines and computers often employ Compact Disk Read-Only Memory (CDROM) media or DVD media for storing large amounts of data such as video or audio data.
In the remainder of this specification, the acronyms CDROM and DVD will be grouped together, and commonly referred to as DVD""s, since the subject matter of this disclosure applies equally to both types of systems.
Typically, DVD""s are the storage media utilized for marketing video and audio products, as well as complex software systems. When a user purchases the product, the user mounts the DVD into a player or reader designed to read the information stored therein, and then causes the read process to begin.
DVD""s store information in digital form, resulting in data that is either a one (1) or a zero (0). Depending on the encoding scheme used when writing the DVD, certain sequences of one""s and zeros are not allowed. For example, in the (2,10) encoding scheme, there must be no less than two consecutive zeros, and there must not be more than 10 consecutive zeros.
Reading and evaluating information stored on a DVD involves a concept called Partial Response Maximum Likelihood (PRML). Briefly, the impulse response of the target read channel is typically described by
H(D)=a+b(D)+c(D2)+d(D3)xe2x80x83xe2x80x83(R. 1)
where a, b, c, and d are coefficients in the relationship.
In prior art systems, these coefficients a, b, c, and d are values which are determined when a test data sequence is read from the DVD when the DVD is first placed in the reader. The values of these coefficients are determined by reading the known test sequence, and then computing the target response many times, using different values substituted for each variable, in order to determine the proper values to use when reading actual data.
While suitable for its intended purposes, the prior art systems must compute the values of four coefficients to minimize the error between the target response and the real system response. The computation of four coefficients takes time and requires complex hardware to accomplish.
Further, prior art systems use threshold detection which allows for wandering of the baseline signal, introducing errors which are caused by the decoding scheme, rather than by the actual read process itself. As DVD speeds increase, tracking the baseline becomes more difficult, and the error rate increases.
It would thus be beneficial to provide a DVD system which requires the computation of fewer variables, thus minimizing the time required to calibrate the system when a new DVD is inserted into the system.
According to a first principle of the present invention, a method is provided for analyzing data read from DVD storage media. According to a second principle of the present invention, a method is provided which minimizes read errors in data read from DVD storage media. According to a third principle of the present invention, a method is provided for performing a difference metric calculation on data read from a DVD storage media.
A method for processing a digitized analog signal read from a DVD media and provided to a digital processing system is described herein. The method includes the steps of forming a first set of data from actual data read from a location on a DVD media, the location containing a known test data sequence, forming a second set of data including the known data bits making, up the known test data sequence. The method proceeds with the steps of comparing the first set of data to the second set of data; and determining the magnitude of no more than two variables, the two variables representing at least three coefficients in an impulse response relationship which models the digital processing system, the magnitude of the no more than two variables being determined so that the error rate between the first and second sets of data is minimized.